1. Field of the Invention
The present invention relates to a unicast-to-multicast converting apparatus, method, computer program product and a monitoring system, and more particularly to a unicast-to-multicast converting apparatus for, method of, and computer program product for converting unicast data packets received from a plurality of monitoring camera units into multicast data packets to be multicast to a plurality of display terminals, and a monitoring system comprising the same.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of monitoring systems comprising a plurality of monitoring camera units each for taking a monitoring image to be converted to monitoring image data and a plurality of display terminals each for converting the monitoring image data taken and converted by one or more of the monitoring camera units into the monitoring image to be displayed wherein the display terminals are connected with the monitoring camera units through networks to ensure that each of the display terminals receives and displays the monitoring images taken and converted by one or more of the monitoring camera units regardless of whether or not the display terminals are placed distant from the monitoring camera units.
The monitoring camera units may be connected with the display terminals through networks such as, for example, IP (Internet Protocol) based networks, hereinlater referred to simply as “IP networks”. The monitoring image data taken and converted by the monitoring camera units may be transmitted to the display terminals through IP networks by means of, for example, broadcast transmissions.
One typical example of a conventional monitoring system of the this type, hereinlater referred to as a “first conventional monitoring system”, is exemplified and shown in FIG. 11 as comprising a plurality of monitoring camera units 101 each for taking a monitoring image to be converted to monitoring image data, and a plurality of display terminals 102 each for converting the monitoring image data into the monitoring image to be displayed wherein the monitoring camera units 101 are connected with the display terminals 102 through a broadcast IP network 103. This means that the monitoring image data taken and converted by the monitoring camera units 101 are transmitted to the display terminals 102 by means of broadcast transmissions.
The first conventional monitoring system, however, encounters a drawback that the monitoring image data taken and converted by the monitoring camera units 101 and transmitted by means of broadcast transmissions is delivered to all of the entities connected with the broadcast IP network 103 including the display terminals 102 and the monitoring camera units 101. This means that the monitoring image data taken and converted by the monitoring camera units 101 and transmitted to the display terminals 102 by means of broadcast transmissions is delivered not only to the display terminals 102 but also to the monitoring camera units 101. The fact that the monitoring image data taken and converted by the monitoring camera units 101 is delivered back to the monitoring camera units 101 results in the unnecessary increase in the load applied to the IP network 103 on the side of the monitoring camera units 101. Furthermore, the first conventional monitoring system encounters another drawback that all of the display terminals 102 can receive the monitoring image data taken and converted by the monitoring camera units 101, thereby making it easy for an unauthorized person to have access to the monitoring image data in the conventional monitoring system through, for example, any one of the display terminals 102.
Alternatively, the monitoring image data taken and converted by the monitoring camera units 101 may be transmitted to the display terminals through IP networks by means of, for example, UDP (User Datagram Protocol) multicast transmissions. One typical example of a conventional monitoring system of this type, hereinlater referred to as a “second conventional monitoring system” is disclosed in, for example, Japanese Patent Laid-open Publication No. 2001-69483. The second conventional moving system is exemplified and shown in FIG. 12 as comprising a plurality of monitoring camera units 101 each for taking a monitoring image to be converted to monitoring image data, an image encoding apparatus 201 for encoding the monitoring image data taken and converted by the monitoring camera units 101 to generate encoded monitoring image data, an encoded image converting apparatus 202 for converting the encoded monitoring image data generated by the image encoding apparatus 201 into encoded monitoring image data in a specified format appropriate for delivering, an image delivering apparatus 203 for delivering the encoded monitoring image data in the specified format converted by the encoded image converting apparatus 202 by means of UDP multicast transmissions, IP router 204 for forwarding the encoded monitoring image data delivered by the image delivering apparatus 203, and a plurality of display terminals 102 each for receiving the encoded monitoring image data forwarded by the IP router 204, and converting the encoded monitoring image data thus received into monitoring images to be displayed.
The IP router 204 may perform UDP multicast protocol control processing in conformance with a protocol such as, for example, IGMP. The IP router 204 is designed to forward the encoded monitoring image data delivered by the image delivering apparatus 203 to a plurality of display terminals 102 in a manner that each of the display terminals 102 receives the monitoring image taken by one of the monitoring camera units 101. This means that each of the display terminals 102 may submit a request to the IP router 204 for forwarding the monitoring image data taken and converted by desired one of the monitoring camera units 101, and the IP router 204 performs UDP multicast protocol control processing to forward the monitoring image data taken and converted by the desired one of the monitoring camera units 101 to the display terminal 102 in response to the request. Each of the display terminals 102 is operative to display the monitoring image converted from the monitoring image data in the encoded forma forwarded by the IP router 204. This leads to the fact that each of the display terminals 102 is required to submit a request to the IP router 204 for forwarding the monitoring image data taken and converted by desired one of the monitoring camera units 101, and the IP router 204 is required to perform UDP multicast protocol control processing in order to switch the monitoring image taken by one of the monitoring camera units 101 to another monitoring image taken by the desired one of the monitoring camera units 101 to be forwarded to and displayed by the display terminal. As a result of this, it takes a lengthy time for each of the display terminals 101 to switch the monitoring image taken by a monitoring camera unit to the monitoring image taken by another monitoring camera unit, thereby degrading the convenience and operability of the monitoring system.
As will be appreciated from the foregoing description, the second conventional monitoring system doe not encounter the aforementioned drawbacks of unnecessarily increasing the load applied to the IP network on the side of the monitoring camera units 101. The second conventional monitoring system, on the other hand, encounters another problem that it takes a lengthy time for display terminals 102 to switch the monitoring image taken by a monitoring camera unit to the monitoring image taken by another monitoring camera unit, thereby causing a delay while switching the monitoring image to be displayed in the display terminals 102 and degrading the convenience and operability of the monitoring system. The present invention is made with a view to overcoming the previously mentioned drawbacks.